Appendix A: Isotope Quick-Reference Cards

These cards cover the isotopes that ANSI N42.34 expects an identifier to recognize, plus the medical and NORM isotopes operators encounter most often. Each card is organized the same way:

Isotope. chemical symbol and mass number
Class. SNM, industrial, medical, NORM
Half-life. operational rule of thumb
Key gamma energies (keV). what the spectrum will show
Common context. where you'll find it
Threat indicator?. when this isotope's presence raises concern

Confirm any operational decision with reachback. The cards are quick reference, not the final word.

Card A.1: Cs-137 (Cesium-137)

Class: Industrial / threat candidate
Half-life: 30.1 years
Key gamma: 662 keV (single, dominant)
Common context: Industrial gauges, food irradiators, well logging, calibration sources, legacy medical (some teletherapy units).
Threat indicator? Yes. Cs-137 outside a licensed industrial context is a major concern. Common in RDD planning scenarios.

Card A.2: Co-60 (Cobalt-60)

Class: Industrial / threat candidate
Half-life: 5.27 years
Key gammas: 1173 keV, 1333 keV (two distinctive lines)
Common context: Industrial radiography, food/medical sterilization, legacy teletherapy, calibration sources.
Threat indicator? Yes if outside licensed context. Co-60's high-energy gammas penetrate shielding and travel far.

Card A.3: Ir-192 (Iridium-192)

Class: Industrial / threat candidate
Half-life: 73.8 days
Key gammas: Multiple peaks; 296, 308, 316, 468, 604 keV
Common context: Industrial radiography (the most common "lost-source" call). Pipe inspection, weld testing.
Threat indicator? Yes if outside licensed context. Frequently the subject of state RCP "missing source" notices.

Card A.4: Am-241 (Americium-241)

Class: Industrial / consumer / threat candidate
Half-life: 432 years
Key gamma: 60 keV (low energy; easily shielded)
Common context: Smoke detectors, density gauges, soil moisture probes, calibration sources, well-logging tools.
Threat indicator? Yes if outside licensed context, especially in quantity. Common in RDD scenarios because of long half-life.

Card A.5: Ra-226 (Radium-226)

Class: NORM / industrial / legacy
Half-life: 1,600 years
Key gammas: Multiple via daughters; 186, 295, 352, 609, 1764 keV
Common context: Antique luminous dials/clocks, oilfield pipe scale, legacy medical, geological samples.
Threat indicator? Generally legacy or NORM. Antique watches and aviation instruments are routine. Pipe scale is routine in oil country. Investigate if outside expected context.

Card A.6: U-235 (Uranium-235)

Class: SNM
Half-life: 7.04 × 10⁸ years
Key gammas: 143, 163, 186, 205 keV
Common context: Reactor fuel, weapons material (HEU = highly enriched uranium > 20% U-235), university research samples.
Threat indicator? Yes, SNM. Especially HEU. Coordinate immediately with federal partners on positive identification.

Card A.7: U-238 (Uranium-238)

Class: Natural / industrial
Half-life: 4.47 × 10⁹ years
Key gammas: Via daughters; 186 keV (overlap with U-235), 1001 keV (Pa-234m), 609/1764 keV (Bi-214)
Common context: Natural uranium ore, depleted uranium (counterweights, ammunition penetrators, ship/aircraft ballast), industrial radiography.
Threat indicator? Less than HEU; still warrants context check.

Card A.8: Pu-239 (Plutonium-239)

Class: SNM
Half-life: 24,100 years
Key gammas: Low and weak; 414, 375, 345 keV (often masked); strongest signature is neutron emission from spontaneous fission of even Pu isotopes.
Common context: Weapons material; reactor-grade Pu samples; pacemakers (legacy); RTG (legacy).
Threat indicator? Yes, SNM. Neutron alarm is the primary indicator on most field instruments. Escalate immediately.

Card A.9: Tc-99m (Technetium-99m)

Class: Medical
Half-life: 6.0 hours
Key gamma: 140 keV (single, dominant)
Common context: Most common medical isotope. Bone scan, cardiac perfusion, sentinel node, brain imaging.
Threat indicator? No. Always verify patient context.

Card A.10: I-131 (Iodine-131)

Class: Medical
Half-life: 8.02 days
Key gammas: 364 keV (dominant), 637 keV
Common context: Thyroid therapy and diagnosis. Patients can alarm portal monitors for days.
Threat indicator? No. Verify patient context. (Note: some industrial uses of iodine isotopes exist; confirm.)

Card A.11: F-18 (Fluorine-18)

Class: Medical
Half-life: 110 minutes
Key gamma: 511 keV (annihilation peak; positron emitter)
Common context: PET imaging (FDG most common). Decays away within a day.
Threat indicator? No. Verify patient context.

Card A.12: Lu-177 (Lutetium-177)

Class: Medical
Half-life: 6.65 days
Key gammas: 113, 208 keV
Common context: Targeted radionuclide therapy in oncology (neuroendocrine tumors, prostate cancer).
Threat indicator? No. Verify patient context.

Card A.13: Ga-67 (Gallium-67)

Class: Medical
Half-life: 78.3 hours
Key gammas: 93, 184, 300, 393 keV
Common context: Inflammation and infection imaging.
Threat indicator? No. Verify patient context.

Card A.14: Tl-201 (Thallium-201)

Class: Medical
Half-life: 73 hours
Key emissions: ~70 keV X-rays, 167 keV gamma
Common context: Cardiac perfusion imaging.
Threat indicator? No. Verify patient context.

Card A.15: I-123 (Iodine-123)

Class: Medical
Half-life: 13.2 hours
Key gamma: 159 keV
Common context: Thyroid imaging, brain imaging.
Threat indicator? No. Verify patient context.

Card A.16: Mo-99 / Tc-99m Generator

Class: Medical
Half-life: Mo-99: 66 hours
Key gammas: 140 keV (Tc-99m daughter), 740 keV (Mo-99)
Common context: Hospital generators, transit between nuclear pharmacies and hospitals.
Threat indicator? No, but generators in unexpected locations warrant investigation.

Card A.17: K-40 (Potassium-40)

Class: NORM
Half-life: 1.25 × 10⁹ years
Key gamma: 1460 keV
Common context: Everywhere. Soil, fertilizer, salt substitute, bananas, granite, the human body.
Threat indicator? No. Always present at low levels.

Card A.18: Th-232 series (Thorium)

Class: NORM
Half-life: 1.4 × 10¹⁰ years
Key gammas (via daughters): 583 keV (Tl-208), 911 keV (Ac-228), 2614 keV (Tl-208)
Common context: Thoriated welding rods, lantern mantles, optical lenses, granite, monazite sand, ceramics.
Threat indicator? No. Routine in many cargo and consumer settings.

Card A.19: U-natural / Ra-226 series

Class: NORM
Half-life: Effectively long (parent)
Key gammas (via daughters): 186 keV (Ra-226 / U-235 overlap), 295/352 keV (Pb-214), 609/1120/1764 keV (Bi-214)
Common context: Oilfield pipe scale, phosphate fertilizer, granite countertops, certain ceramics.
Threat indicator? No. Cargo context confirms.

Card A.20: Eu-152 (Europium-152)

Class: Industrial / calibration
Half-life: 13.5 years
Key gammas: Multi-line: 122, 244, 344, 779, 964, 1112, 1408 keV
Common context: Calibration sources for spectroscopy.
Threat indicator? Generally low; investigate if outside laboratory context.

Card A.21: Ba-133 (Barium-133)

Class: Industrial / calibration
Half-life: 10.5 years
Key gammas: 81, 276, 303, 356, 384 keV
Common context: Calibration sources, some industrial uses.
Threat indicator? Low.

Card A.22: Sr-90 / Y-90

Class: Industrial / medical
Half-life: 28.8 years (Sr-90) / 64 hours (Y-90)
Key emissions: Pure beta, gammas only via bremsstrahlung
Common context: Industrial gauges, eye-cancer therapy, radioisotope thermoelectric generators (legacy).
Threat indicator? Difficult to identify with a gamma RIID; suspect if a survey meter shows beta but RIID gives ambiguous gamma ID.

Card A.23: Cf-252 (Californium-252)

Class: Industrial / SNM-adjacent
Half-life: 2.65 years
Key emissions: Strong neutron source; some gammas
Common context: Well logging, industrial neutron sources, calibration.
Threat indicator? Yes if outside licensed context. Strong neutron alarm.

Card A.24: Ho-166m

Class: Industrial
Half-life: 1,200 years
Key gammas: 184, 280, 711, 810 keV among many
Common context: Calibration sources, some industrial uses.
Threat indicator? Low.

Card A.25: H-3 (Tritium)

Class: Industrial / consumer
Half-life: 12.3 years
Key emissions: Pure low-energy beta, not detected by gamma RIID
Common context: Self-luminous exit signs, watch faces, gun sights, fusion research.
Threat indicator? Low. Not a concern for RIID alarm. Listed for operator awareness.

Card A.26: Co-57

Class: Medical / calibration
Half-life: 271 days
Key gammas: 122, 136 keV
Common context: Cardiac imaging, calibration sources for low-energy spectroscopy.
Threat indicator? Low.

Card library note: This list is the operator's working set. Reachback maintains a much larger library and can address isotopes not on these cards.